Four nocturnal desert tenebrionids with complete ecological niche overlap as adults form daytime aggregations in burrows in species pairs, Eremostibes with Parastizopus and Herpiscius with Gonopus. Parastizopus and Gonopus were the primary burrowers, the associations being initiated by the smaller partners. Association was not dependent on differences in temperature preference between species nor only on the ecological conditions the larger beetles provided. Partner species were preferred over other tenebrionids of the same size. The proximate segregating mechanism was avoidance of the non-partner by the smaller species. Avoidance was odour-mediated in Eremostibes, which also showed an equal odour-based preference for conspecifics and Parastizopus. Odour profile similarity between the two was hypothesized as the mechanism permitting coexistence. An odour-mediated preference for Gonopus or conspecifics could not be shown for Herpiscius, nor was Parastizopus odour avoided. Here, a higher relative humidity in inhabited burrows was suggested as the proximate factor promoting association. A possible advantage of aggregation for desert tenebrionids is discussed.